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Air travel activates clotting more than immobilization alone, especially in patients with factor V Leiden (fVL) and/or oral contraceptive use

Investigators in the Netherlands evaluated the effects of air travel and prolonged immobilization on the ground on indicators of clotting activation in 71 patients (11 with fVL, 15 using oral contraceptives, 15 who had both fVL and used oral contraceptives, and 30 patients who did not have fVL and did not use oral contraceptives). The indicators of clotting activation that were measured before and after each intervention were thrombin-antithrombin complex (TAT), fragment 1+2 (F 1+2), and d-Dimer. These indicators were measured at base line and before and after 3 interventions: an 8 hr plane flight, an 8 hr movie marathon, and 8 hrs of "daily life situation." TAT was the indicator that exhibited the greatest increase of approximately 30% after the flight vs. decreases of 2% and 7.9% after the movie marathon and daily life situation, respectively. High responders for any of the indicators (defined as those whose indicator levels were at least 3 standard deviations above the mean value for the daily life situation period) were found in 17% of individuals after air travel vs. 3% after the movie marathon and only 1% after daily life situation. Four individuals were high responders for all three indicators after the flight, but no individuals were high responders for all three indicators after the movie marathon or daily life situation. The presence of fVL or oral contraceptive use increased the likelihood of having elevated indicators and the combination of both factors appeared to be at least additive. For example, 6 of 14 (43%) of patients with fVL and oral contraceptive use were found to be high responders after the flight vs.17% for the entire group. The authors suggest that the low air pressure and/or low oxygen level in planes during travel may increase the risk of clotting over that observed with immobilization on the ground. Further, patients with fVL and users of oral contraceptives may be at increased risk. Even so, the absence of fVL and oral contraceptive use does not exempt individuals from this risk as evidenced by the fact that the two women with the highest TAT levels after the flight did not have fVL and were not taking oral contraceptives.